Pyridazonylphosphoric acid derivatives as herbicides

ABSTRACT

Phosphoric and thiophosphoric-diester-N-(1-phenyl-5-halogeno6(1H)-pyridazonyl-(4))-amides possess selective herbicidal properties. They can be used for combating grass-like and dicotyledonous weeds in useful plants.

United States Patent [191 Bader, deceased et al.

[4 1 Sept. 23, 1975 41 PYRIDAZONYLPHOSPHORIC ACID DERIVATIVES AS HERBICIDES [75] Inventors: Jiirg Bader, deceased, late of Arlesheim, Switzerland; by Dagmar Bader-Ludwig', legal representative, Arlesheim, Switzerland [73] Assignee: Ciba-Geigy Corporation, Ardsley,

221 Filed: Sept. 26, 1974 21 1 Appl. No.: 509,628

Related US. Application Data [62] Division of Ser. No. 296,428, Oct. 10, 1972, Pat. No.

[56] References Cited UNITED STATES PATENTS 3,823,142 7/1974 Bader et al. 7l/86 3,849,103 11/1974 Harris et al. 71/8 OTHER PUBLICATIONS Kirsonov et al., Chem. Abs., Vol. 51, 1821-1822(b) (1957). Kabachnik et al., Chem. Abs., Vol. 51, 1823(b) (1957). Konecny et al., Chem. Abs. Vol. 77, I972 620l6(h).

Primary Examiner-James O. Thomas, Jr. Attorney, Agent, or Firm-Frederick H. Rabin 57 ABSTRA CT Phosphoric and thiophosphoric-diester-N-[ l-phenyl-S- halogeno-6( lH)-pyridazonyl-(4)l-amides possess selective herbicidal properties. They can be used for combating grass-like and dicotyledonous weeds in useful plants.

10 Claims, No Drawings PYRlDAZONYLPl-IOSPHORIC ACID DERIVATIVES AS HERBICIDES This is a division of application Ser. No. 296,428 filed on Oct. 10, I972, now U.S. Pat. No. 3,853,870.

The present invention relates to new l-phenylpyridazonylphosphoric acid derivatives, a process for their manufacture, also to herbicidal agents which con tain these new compounds as active substances, and to .a method of combating grass-like and dicotyledonous weeds, which comprises the use of the new substances or of agents which contain them.

The new active substances are phosphoric and thiophosphoric-diester-N-[ l-phenyl--halogeno-6(1H)- pyridazonyl-(4)]-amides of the formula I:

"will rine; the 2-chloroethoxy radical is preferred. A'lkylthio radicals R and R, also contain l to 4 carbon atoms, such as methylthio, ethylthio, n-. and isopropylthio and the various butylthio radicals.

Preferably, the radicals R and R, are identical.

The new pyridazonylphosphoric acid derivatives are manufactured according to the present invention by treating a l-phenyl-pyridazone derivative of the formula ll R x 2} i /Nl (II) in which R, R, and X have the meanings given under formula I and R represents a radical which may at least be partially split off, namely an optionally halogenated alkoxy, alkenyl or alkylthio radical, with an acid or base, optionally in the presence of water and/or an organic solvent, and isolating the end product of the formula 1 from the reaction mixture.

As a rule the process is carried out either with aque' ous acids or bases, or water is added to the reaction mixture before the working up. In this case the entire radical R is split off by hydrolysis. If R is an alkoxy or alkenyloxy radical, it is also possible to use concentrated aqueous hydrochloric acid or anhydrous hydrohalic acid as acid in organic solvents. In this case alkyl halide or alkenyl halide is then split off and the oxygen atom of thealkoxy group remains at the phosphorous atom.

The method is known and is described, for example, in Chem. Abstr. 51, 1823.

The starting materials of the formula ll and their manufacture are described in Swiss patent application No. 18554/ or in Belgian Pat. Spec. No. 776,660. They are obtained from the corresponding l-phenyl-4- azido-5-hal ogeno-6( ll l)-pyr idazo nes (US. Pat. No. 3 210 354 and Chem. Abstr. 70, 47382 m) by reaction with phosphites of the formula ganic solvents) hydrogen chloride or hydrogen bromide, dilute perchloric acid, dilute nitric or sulphuric acid, sulphurous acid, phosphoric acid, diphosphoric acid, polyphosphoric acids, and partially esterified sulphuric and phosphoric acids.

As examples of organic acids there may cited: acetic acid, propionic acid, formic acid, pivalic acid, oxalic acid, nitrobenzoic acids, chloroacetic acid, chlorinated benzoic acids, sulphonic acids, such as methanesulphonic acids, cthanesulphonic acid, aromatic sulphonic acids, for example of substituted benzene, phosphonic acids and phosphinic acids such, for example, as chloromethanephos phonic acid, diphenylphosphinic acid. As examples of further organic compounds which have acid reaction there may be mentioned phenols, in particular phenols substituted by chlorine and/or nitro groups, and also ion exchangers.

Instead of acids, it is also possible to carry out the reaction with inorganic or organic bases. Exemplary of inorganic, preferably aqueous, bases are: the hydroxides of alkali and alkaline earth metals, such as NaOH, KOH, Ca(OH) Ba(OH) and NH OH, also salts of basic reaction, such as sodium bicarbonate, sodium hydrogen carbonate, potassium carbonate, trisodium phosphate, also basic ion exchangers.

The application concentrations depend upon the kind of acid or base used: in the case of stronger acids or bases catalytic amounts suffice, for example 0.05 molar equivalents of 5% sulphuric acid, but larger .of the acid used. Stronger acids possess the advantage that, when used in sufficiently large excess, they dissolve the reaction products, which then can be precipitated by dilution with water.

Additional examples of solvents and diluents are: alcohols, such as methanol, ethanol, isopropanol, 2- methoxyethanol, benzyl alcohol; ethers, such as diethyl ether, l,2-dimethoxyethane, 2,2-dimethoxy-diethyl ether, dioxan, tetrahydrofuran; amides, such as dimethyl formamide, hexamethylphosphoric triamide, formamide, sulphoxides andsulphones, such as diemthyl sulphoxide or tetramethylenesulphone; esters, such as ethyl acetate, ethyl formylate; aromatic or aliphatic, optionally chlorinated or otherwise substituted hydrocarbons, such as toluene, chlorobenzene, xylene, nitrobenzene, methylene chloride, dichloroethylene.

The reaction conditions depend upon the acid or base used and are to be so chosen that a continuing saponification of the molecule, for example the splitting off of the phosphoric ester radical, is avoided. The reaction temperatures may be from -50C to 120C and the reaction times from a few seconds to several days. In this connection, however, the stronger the acid or base used and the greater the concentration of the acid or base, the shorter the reaction times and the lower the temperatures chosen will be. For example, it is expedient to keep a reaction temperature of below 25C when using concentrated hydrochloric acid.

The conditions being suitably chosen, the formation of the end products I is always the preferred reaction step, since it proceeds very much more easily than other possible hydrolysis reactions at the compounds of the formulae II and I.

According to a further process, it is also possible to manufacture the newpyridazonylphosphoric acid derivatives of the formula I by reacting a 1-phenyl-4- amino-5-halogeno-6(1I-I)-pyridazone of the formula III in which X represents chlorine or bromine, if need be in the presence of a base in a solvent, e.g., chloroben zene, with a phosphoric or thiophosphoric diester chloride of the formula IV 'the new l-phenyl-pyridazonyl-phosphoric acid derivatives ofthe formula I.

EXAMPLE I 7.8 g of l-phenyl-4-(trimethoxyphosphoranylideneamino)-5-bromo-6( l H)-pyridazone are finely pulverised and,.while stirring, charged within 2 minutes in small amounts into 12 ml of 35% hydrochloric acid. The substance dissolves while foaming. Then about 30 g of ice-water mixture are added, in the process of which the reaction product falls out as a resin. It is decanted and washed twice with water, then 10 ml of isopropanol are added and the product is crystallised by rubbing with a glass rod. The product is filtered with suction and recrystallised from' a small amount of methanol to give about 6 g of 0,0-dimethyl- N-( l-phenyl-5-bromo-6( 1H )-pyridazon-4-yl)- phosphoric diester amide in the form of colourless crystals with a melting point of l40-l42C (compound No. 1).

EXAMPLE 2 EXAMPLE 3 5 .0 g of finely pulverised l-phenyl-4- (trimethoxyphosphoranylidene-amino(-5-bromo- 6(1I-I)-pyridazone are whirled at 15C with acetic acid until complete solution occurs (about 1 minute). The reaction product is then precipitated with icewater and further processing is carried out as described in Example 1 to give likewise the end product of Examples l and 2 (melting point: 136-l40C).

EXAMPLE 4 6.0 g of l-phenyl-4-(trimethoxyphosphoranylideneamino )-5-bromo-6( 1H)-pyridazone are dissolved in a mixture of 15 ml of methanoland 15 ml of l,2-dimethoxyethane. A solution of 0.7 g of sodium hydroxide in 3 ml of water is added and the mixture is left to stand for 15 hours. It is then neutralised by addition ofa small amount of glacial acetic acid and evaporated. The residue is dissolved in acetone and undissolved sodium acetate is filtered off. Column chromatography on silica gel and recrystallisation from methanol yield once again 0,0-dimethyl-N-( l-phenyl- 5-bromo-6-( l H )-pyridazon-4-yl )i-phosphoric amide which melts at l4l-142C.

EXAMPLE 5 diester which were manufactured according to the processes described in the preceding Examples:

(Chenopodiaceae), slender foxtail (alopecurus spp.) and other foxtail species, e.g., Amarantus spp., grasses, e.g., Lolium spp., Compositae, e.g., Taraxacum spp., camomile species (Matricaria spp.), are destroyed or hindered in their growth without damage being caused to cultivated plants, such as cereals, maize, cotton, sorghum, soya beans and sugar beet. The rates of application vary and are dependent on the time of application; they are between 0.1 to 10 kg of active substance per hectare, on preemergence application up to 1 kg per hectare and on postemergence 3 to 10 kg of active sub stance per hectare. In order to totally destroy entire crops of weeds, for example on fallow land neighbouring on the cultivated areas, it is necessary to use more than 10 kg per hectare. The usual crop rotation may proceed on application of the new active substances without any detrimental effects.

In low concentrations the active substances of the formula I also possess plant growth regulating properties.

HERBICIDAL ACTION ON APPLICATION BEFORE GERMINATION OF THE PLANTS (PREEMERGENCE APPLICATION) In a greenhouse the active substance is sprayed in the form of an aqueous solution of a wettable powder con- The new l-phenyl-pyridazonyl-phosphoric acid derivatives are stable compounds which are more readily soluble in organic solvents than the phenylpyridazone derivatives hitherto known as herbicidally active (e.g., German Auslegeschrift No. 1,105,232 this constitutes an important advantages The pyridazone derivatives of the formula I possess excellent herbicidal properties and are suitable in particular for combating grass-like and latifoliate weeds in various crop plant cultures. When used in high concentrations the new compounds act as total herbicides; on the other hand, when used in lower concentrations they act as selective herbicides. Deep rooted, difficultly combattable weeds which are one or more years old are successfully damaged in their growth or destroyed by the active substances of the formula I. The new active substances can he appliedwith the same good success before germination (preemergence) and after germination (postemergence). Thus meadow weeds. for example millet species (Panicum spp.), mustard species centrate on containers with meadow soil. A number of test plants from the following group are sown into the thus prepared soil:

a: Alopecurux m \'0suruides b: Poa annuu c: Selaria imlica d: Avena falua e: Lolium perenne f Digilaria sanguinall's g: Stellaria media h: Echinochlua 2) Cultures:

A= maize (Zea mayx) B= cotton (Gossypium) i: Sinapis alba k: Clzenopodium l: Sesbania exellam m: Amaramhux retruflexus n:Chrysan1lzenum Ieucatrichum o: lpomaea purpurea p: Galium apurine q: Paslinaca saliva C= sugar beet (Bela) D= sorghum E= soya (Glycine) 7 I I 8 Rating: and cationic surface active substances," which for exam 9 plants undamaged control ple improve the adhesion of the active'ingredients on plants died plants or parts of plants (adhesives and agglutinants) 2-8 intermediate stages of damage and/or ensure a better wettability twetting age ts) and not tested 5 dispersibili'ty ("diSp'ei'sihgagentsQ. Examplesof suitable r I adhesives are theflfollo'wing: olein/chalk n iixt'ure, eellu l the enable powdercqlceltrate lose" derivatives (methyl cellulose, caribox'yrn ethyl ce'llv parts of active substance, 0;6 part of sodium l lg hhyd b y ihyl gly l h 'i-g of lkyl and dibutylnaphthalenesulphonate, -l part of naphthalene digikyl' hehblghiivifj '5 {O 1 e hylen Xider adibals sulphonic aci-d/phenolsulphonic acid/formaldehyde r0 f i qi g f 't) a 'a' om h h aik di; condensate .(3:2:l ),-l O parts of sodium aluminium sili-' 31' hgrnin suiphdhiq d h i l alijf je tg l h' 1kg Cate, Parts of Chma yli'neearth metal salts, polyethylene glycol ethers (car-v The herbicidal agents are manufactured by mixing bowaxes),"fatty alcohol polyethylene glycol ethers havthe active substances with'suitable carriers'and/or dising 5 to ethylene oxide radicals per molecule and 8 persing agents-- In' orderto broaden-the activity? specto 18 carbon atoms in the fatty alcohol moiety, condentrum it is possible to add to; these agents still other her- 7 sation products of ethylene oxide/propylene oxide, polbicilclleahfolr examg le from the series cl lgthe trigzipkes, yvinyl pyrro lidones, polyvinyl aleohols, QZHCTHIIZIItiOH suc as aogenoiamino-s-tr az nes,a oxyan a yproducts of ureav and, -formaldeh-yde, arr asos atex; lthio-diamino-s-triazines, such as uraciles, aliphatic products, carboxylic acids and halogenocarboxylic acids, haloge' The water-dispersible concentrates of the active subnated benloic acids and Phenylacetic acids, aryloxyalk' stance, i.e., wettable powders, pastes and amulsifiable anecarboxylic acids, hydrazides, amides, nitriles, esters concentrates, are agents which can be diluted i of such earboxylic acids, carbamic acids and thiocarwatgh to any cohcem-tahiozn-desired' They'chnsist f a bamc aclds, urea, tive substance, carrierfoptionally additives which stabii accordmg m i 7 lize the active substance, surface-active substances and ture ll'l nown manner y intimate y mixing an or anti foam agents and, optionally, l i actlve subsfancgs g i ggR I the Wettable powdersaridfpastes are obtained by mixing 6 g g 6 g' and grindi'ng"the"aetive. substances withdispersing i S or f ig Q. 1c a men owarbst e "l g Su 5 agents and pul-verul ent carriers in suitable apparatus S z i F? e aval a e an until homogeneity'is' attained. Carriers are, for examgg l 2.5 m e O owmg Orms' ple, those mentioned for the solid forms of application.

I r 40 In some cases it is advantageous to use mixtures of difdusts, tracking agents, granules, coated granules, im-

regnated granules and homogeneous granules ferent carriers. As dispers ng agents there can be used,

Li forms for example, condensation products of su'lphonated q naphthalene and sulphonated naphthalene derivatives a. active substances which are dispersible in water.

. with formaldehyde, condensation products of naphthawettable powders, pastes, emulsions,

b Solutions lene or naphthalene sulphonic acids with phenol and To manufacture solid forms (dusts, tracking agents), fp 1 T iT q i q g:- the active substances are mixed with; solid-carriers. 5 9 ?;.Q v m P Ti -U Suitable carriers are, for example:' kaolin, talcum, bo- :2 K a Mi n za g lus, loess, chalk, limestone, ground limestone, :attaclay, v5 1 5% a a i 'i f "fi dolomite, diatomacous carth, precipitated silica, alka- 9%: a o 2 line earth silicates, sodium and potassium aluminum a i $9,? fiai g a silicates (feldspar and mica), calcium and magnesium p i y a 0 g lf zn 11 l t sulphates, magnesium oxide, grounds'yntheticjn ateri- 5 q f iit 3, Plip fl r i y als,fertilisers, for example ammonium sulphate,- ammon fi g g f l p i i g?! Ti nium phosphate, ammonium nitrate, urea, ground vegwt 9 i z 7, 19"; a etable products, such as corn meal, bark dust, sawdust, f i 1 5 nutshell meal, cellulose powder, residues of plant ex-' S tab ant oamagen 1? slllconeS-i tractions, activated charcoal, etc. These substances can The active substances are so mixed, ground sieved either be used alone or in admixture with one another. 0' and strained withithe additives mentioned :above that,::

The particle size of the carriers for dusts is'advantain wettablepowderathe solid particle size of from 0.02 geously up to about 0.1 mm, for tracking agents from to .0.Q4 and in pastes, of, 0 ,03 ,is not .exeededflo, pro-v about 0.075 to 0.2 mm, and for granules 0.2 mm or ducei emulsifia-ble concentrates andpastes,=;dispersing larger. h I agents such as those given in the previousparagraphs, v.

The solid forms contain the active substances inconorganic solvents and water-are usedrExaniplesof suite centrations from 0.5 to e To these mixtures canalso be added additives which stabilize the active substance and/or non-ionic, anionic able solveiitsare the-following: alcohqls benzcne Xy-i, lenes, toluene dimethyl sulphoxide, and. mineral oilitraction's boiling between l20and 350C. The solvents must be practically odorless, not phytotoxic, inert to the active substances and not readily inflammable.

Furthermore, the agents according to the invention can be applied in the form of solutions. For this purpose the active substances or several active substances of general formula II are dissolved in suitable organic solvents, mixtures of solvents or in water..Aliphatic and aromatic hydrocarbons, chlorinated derivatives thereof, alkyl naphthalenes and mineral oils alone and mixed with each other, can be used as organic solvents. In addition to fungicidal active substances, the agents described according to the invention can be mixed with other biocidally active substancesor agents. Thus in order to broaden the activity spectrum the new agents may contain, for example, insecticides, fungicides, bactericides, fungistatics, bacteriost'atics or nematocides,

in addition to the cited compounds of the formula I.

The agents according to the invention may also contain plant fertilisers, trace elements etc.

The active substances of the formula I can, for example, be formulated as follows. The parts denote parts by weight.

Granules The following substances are used to manufacture granules:

5 parts of 0,0-dimethyl-N-[ l-phenyl-S-bromo- 6( 1H)-pyridazonyl-(4)]-phosphoric diester amide,

025 parts of epichlorohydrin,

0.25 parts of cetyl polyglycol ether,

3.50 parts of polyethylene glycol ether,

91 parts of kaolin (particle size: 0.3-0.8 mm).

The active substance is mixed with epichlorohydrin and the mixture dissolved in 6 parts of acetone, then polyethylene glycol ether and cetyl polyglycol ether are added. The resulting solution is sprayed on kaolin and then evaporated in vacuo.

Wettable Powder The following consituents are used to manufacture (a) a 50%, (b) a 25% and (c) a 10% wettable powder:

a. 50 parts of 0,0-diethyl-N-[ l-phenyl-S-chloro- 6( lH)-pyridazony1-(4)]-phosphoric diester amide, 5 parts of sodium dibutylnaphthalene sulphonate, 3 parts of naphthalenesulphonic acid/phenolsulphonic acid/formaldehyde condensate (3:2:1), parts of kaolin, 22 parts of Champagne chalk;

b. 25 parts of S,S'dimethyl-N-[ l-phenyl-S-bromo- 6(lH)-pyridazonyl-(4)]-dithiophosphoric diester amide,

5 parts of sodium oleylmethyltauride,

2.5 parts of naphtalenesulphonic acid/formaldehyde condensate,

0.5 part of carboxymethyl cellulose,

5 parts of neutral potassium aluminium silicate,

62 parts of kaolin; c. 10 parts of 0,0-dimethyl-N-[i-phenyl-S-chloro- 6(lH)pyridazonyl-(4)]-phosphoric diester amide, 3 parts ofa mixture of the sodium salts of saturated fatty alcohol sulphates,

5 parts of naphtalenesulphonic acid/formaldehyde condensate,

82 parts of kaolin.

The indicated active substance is applied to the corresponding carriers (kaolin and chalk) and then these are mixed and ground, to yield wettable powders of excellent wettability and having an excellent capacity for forming suspension. By diluting these wettable powders 10 with water it is possible to obtain suspensions of every desired concentration of active substanceysuch suspensions are used for combating weeds and grasses in crops of cultivated plants. Paste i The following substances are used to manufacture a 45%paste: i

45 parts of 0,0-dimethyl -N-[ l-phenyl-S-bromb- 6( l H)-pyridazonyl-(4 )j-phosphoric diester amide.

5 parts of sodium aluminium silicate,

14 parts of cetyl polyglycol ether with 8 mols of ethylene oxide.

1 part of oleyl polyglycol ether with 5 mols of ethylene oxide, I

2 parts of spindle oil,

10 parts of polyethylene glycol,

23 parts of water. i

The active substance is intimately mixed with the addition in appropriate devices and ground. A paste is obtained from which, by diluting it with water, is possible to manufacture suspensions of every desired concentration of active substance. The suspensions are suitable for treating vegetable plantations.

Emulsion Concentrate To manufacture a 25% emulsion concentrate 25 parts of S,S-dimethyl-N-[l-phenyl-S-bromo- 6( lH)-pyridazonyl-(4)l-dithiophosphoric diester amide,

5 parts of a mixture of nonylphenolpolyoxyethoxyethylene and calcium, dodecylenesulphonate,

35 parts of 3,5,5-trimethyl-2-cyclohexan-l-one,

35 parts of dimethyl formamide,

are mixed together. This concentrate can be diluted with water to give emulsions in desired concentrations. Such emulsions are suitable for combating weeds in crops of cultivated plants, e.g., cotton, maize, sugar beet.

We claim:

1. A herbicidal agent for combating monocotyledonous and dicotyledonous weeds in cultures of crop plants, which, in addition to dispersing agents and/or other carriers, contains as active component an effective amount of a l-phenyl-pyridazony[phosphoric acid derivative of the formula wherein each of R and R independently represents alkoxy of from I to 4 carbon atoms, alkylthio of from 1 to 4 carbon atoms, halogenoalkoxy of from 1 to 4 carbon atoms or alkenyloxy of 3 or 4 carbon atoms, or both together represent an oxyethyleneoxy bridge, and X represents chlorine or bromine.

2. A herbicidal agent according to claim 1, wherein R and R are identical.

3. A herbicidal agent according to claim 1, which contains as active component 0,0-dimethyl-N-[ lphenyl-5-bromo-6( l H)-pyridazonyl-(4)]-dithiophosphoric diester amide.

wherein each of R and R independently represents alkoxy of from 1 to 4 carbon atoms, alkylthio of from 1 to 4 carbon atoms, halogenoalkoxy of from 1 to 4 carbon atoms or alkenyloxy of 3 or 4 carbon atoms, or both together represent an oxyethyleneoxy bridge, and X represents chlorine or bromine.

7. A method according to claim 6 in which R and R are identical.

8. Amethod according to claim 7 in which the compound is 0,0-dimethyl-N-[ l-phenyl-5-bromo-'6( 1H)- pyridazonyl-(4)]-dithiophosphoric diester amide.

- 9. A method according to claim 7 in which the compound is S,S-dimethyl-N-[l-phenyl-5-bromo-6(1H)- pyridazonyl-(4)]-dithiophosphoric diester amide.

10. A method according to claim 7 in which the compound is 0,0-diethyl-N-[ l-phenyl-5-bromo-6( 1H)- pyrida'zonyl-(4)]-phosphoric diester amide. 

1. A HERBICIDAL AGENT FOR COMBATING MONOCOTYLEDONOUS AND DICOTYLEDONOUS WEEDS IN CULTURES OF CROP PLANTS,WHICH, IN ADDITION TO DISPERSING AGENTS AND/OR OTHER CARRIERS, CONTAINS AS ACTIVE COMPOUND AN EFFECTIVE AMOUNT OF A 1-PHENYLPYRIDAZONYLPHOSPHORIC ACID DERIVATIVE OF THE FORMULA
 2. A herbicidal agent according to claim 1, wherein R and R1 are identical.
 3. A herbicidal agent according to claim 1, which contains as active component O,O-dimethyl-N-( 1-phenyl-5-bromo-6(1H)-pyridazonyl-(4))-dithiophosphoric diester amide.
 4. A herbicidal agent according to claim 1, which contains as active component S,S-dimethyl-N-(1-phenyl-5-bromo-6(1H)-pyridazonyl-(4))-dithiophosphoric diester amide.
 5. A herbicidal agent according to claim 1, which contains as active component O,O-diethyl-N-(1-phenyl-5-bromo-6(1H)-pyridazonyl-(4))-phosphoric diester amide.
 6. A method of combating undesirable plant growth in cultures of crop plants, which comprises applying to said cultures a herbicidally effective amount of a compound of the formula
 7. A method according to claim 6 in which R and R1 are identical.
 8. A method according to claim 7 in which the compound is O,O-dimethyl-N-(1-phenyl-5-bromo-6(1H)-pyridazonyl-(4))-dithiophosphoric diester amide.
 9. A method according to claim 7 in which the compound is S,S-dimethyl-N-(1-phenyl-5-bromo-6(1H)-pyridazonyl-(4))-dithiophosphoric diester amide.
 10. A method according to claim 7 in which the compound is O,O-diethyl-N-(1-phenyl-5-bromo-6(1H)-pyridazonyl-(4))-phosphoric diester amide. 